Functionalization of boron dipyrrin (BODIPY) dyes through iridium and rhodium catalysis: A complementary approach to α-and β-Substituted BODIPYs

Article abstract of DOI:10.1002/chem.200802541

Iridium-catalyzed direct borylation has been applied to mesosubstituted dipyrromethane and boron dipyrrin (BODIPY) dyes. Borylation is highly regioselective and complementary: It occurs exclusively at the α position for meso-mesityldipyrromethane and at t

Full text of DOI:10.1002/chem.200802541

DOI: 10.1002/chem.200802541
Functionalization of Boron Dipyrrin (BODIPY) Dyes through Iridium and
Rhodium Catalysis: A Complementary Approach to a- and b-Substituted
BODIPYs
Jinping Chen,[a] Masatoshi Mizumura,[a] Hiroshi Shinokubo,*[b] and Atsuhiro Osuka*[a]
Abstract:
Iridium-catalyzed
direct
thesized. Introduction of a,b-enoate
and a,b,g,d-dienoate functions into
BODIPY dyes at the a or b positions
was achieved by rhodium-catalyzed
Heck-type addition of the borylated
compounds to acrylate and 2,4-penta-
dienoate esters. This functionalization
has a significant effect on the electron-
ic properties of BODIPY dyes, as seen
in substantial redshift of the absorption
and emission spectra. Comparative
studies showed that the a- and b-sub-
stituted series of BODIPY dyes show
substantially different photophysical
properties, and thus the importance of
the position to be functionalized is
highlighted.
borylation has been applied to meso-
substituted dipyrromethane and boron
dipyrrin (BODIPY) dyes. Borylation is
highly regioselective and complementa-
ry: it occurs exclusively at the a posi-
tion for meso-mesityldipyrromethane
and at the b positions for meso-mesityl
BODIPY dye. This regioselective bory-
lation enables a variety of a- and b-
substituted BODIPY dyes to be syn-
À
Keywords: boron · C C coupling ·
dyes/pigments · iridium · rhodium
Introduction
shira coupling,[8] Knoevenagel-type condensation,[9,2b] and
[10]
À
palladium-catalyzed direct C H functionalization.
Other
Boron dipyrrins (BODIPYs) have received much interest in
research areas such as labeling reagents,[1] fluorescent
switches,[2] chemosensors,[3] light-harvesting systems,[4] and
dye-sensitized solar cells[5] owing to their advantageous pho-
tophysical properties such as photostability, high absorption
coefficients, and high fluorescence quantum yields.[6] Fur-
thermore, BODIPY dyes are amenable to modifications,
which allow fine-tuning of properties by introduction of suit-
able substituents at appropriate positions of the dipyrrin
framework. One of the challenges has been the synthesis of
BODIPY derivatives that emit at longer wavelengths with
high fluorescence quantum yields. Post-modification meth-
ods used to attain this goal include halogenation,[7] Sonoga-
strategies, such as replacement of the meso carbon atom by
a nitrogen atom[11] and extension of the p conjugation by
the fusion of aryl moieties with isoindole[12] or furan,[13] are
also quite useful.
Recently, iridium-catalyzed direct borylation of aromatic
À
compounds via C H bond activation has proved to be a
powerful tool for organic synthesis.[14] In addition, the use of
organoboranes with rhodium catalysis has been extensively
[15]
À
explored for new types of C C bond formation. We have
applied these novel metal-catalyzed methodologies to por-
phyrin chemistry, and established highly regioselective iridi-
um-catalyzed b-borylation of porphyrins.[16] Facile introduc-
tion of a,b- and a,b,g,d-unsaturated ester functions into por-
phyrins has also been achieved by rhodium-catalyzed Heck-
type addition of borylated porphyrins to acrylate and 2,4-
pentadienoate esters.[17]
[a] Dr. J. Chen, M. Mizumura, Prof. Dr. A. Osuka
Department of Chemistry, Graduate School of Science
Kyoto University
Here we focus on BODIPY as a substrate for functionali-
zation by a similar strategy. BODIPY and porphyrin have
the same dipyrrin building blocks and both have b-pyrrolic
positions. We anticipated that a combination of iridium-cata-
lyzed borylation and rhodium-catalyzed Heck-type addition
would also be applicable to BODIPY dyes and offer
method for functionalization of BODIPYs with fine-tuned
photophysical properties. Here we disclose a- and b-selec-
tive functionalization of BODIPYs, which allow a direct
Sakyo-ku, Kyoto 606-8502 (Japan)
Fax : (+81)75-753-3970
E-mail: osuka@kuchem.kyoto-u.ac.jp
[b] Prof. Dr. H. Shinokubo
Department of Applied Chemistry, Graduate School of Engineering
Nagoya University
Chikusa-ku, Nagoya 464-8603 (Japan)
Fax : (+81)52-789-5113
E-mail: hshino@apchem.nagoya-u.ac.jp
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Chem. Eur. J. 2009, 15, 5942 – 5949

FULL PAPER
comparison between a- and b-extended conjugation for
BODIPY dyes.
Results and Discussion
Synthesis of the BODIPY dyes: The meso-mesityl dipyrro-
methane 4 and meso-mesityl BODIPY 1 were synthesized
according to the reported procedures.[18] Inspired by boryla-
tion of pyrrole,[19] we examined borylation of 4 (Scheme 1).
Scheme 2. Rhodium-catalyzed addition to acrylate esters.
romethane
5 with hexyl acrylate in the presence of
[{Rh(OH)(cod)}2] as catalyst in dioxane/water (10/1) at
AHCTUNGTRENNUNG
1008C afforded the desired a,a’ double addition products as
a mixture of E,E isomer 9 and E,Z isomer 9’. On the other
hand, the corresponding reaction of diborylated BODIPY 7
furnished a,a’-diacrylate BODIPY 3b in 32% yield along
with partially saturated compound 3b’. Unfortunately, the
borylated products are not stable enough for purification by
column chromatography on silica gel and should be purified
by preparative GPC-HPLC. To eliminate tedious separation
and decomposition of the products on silica gel, we then de-
veloped a procedure for the synthesis of BODIPY dyes
without separation of the borylated intermediates.
Scheme 1. Regioselective borylation of dipyrromethane 4 and BODIPY
1. pin=pinacolato.
Treatment of
(2.0 equiv) in the presence of a catalyst generated from [{Ir-
(OMe)(cod)}2] (1.0 mol%; cod=1,5-cyclooctadiene) and
4 (1.0 equiv) with bis(pinacolato)diboron
A
ACHTUNGTRENNUNG
4,4’-di-tert-butyl-2,2’-bipyridyl (dtbpy, 2.0 mol%) in dioxane
provided a,a’-diborylated product 5 in high yield (80%)
with perfect regioselectivity at the a positions. About 15%
of monoborylated compound 6 was also obtained. The same
strategy was applied to BODIPY 1, but diborylated com-
pound 7 was isolated only in about 20% yield. Although the
yield was not as high as that of meso-substituted dipyrro-
To prepare a-substituted BODIPYs, meso-mesityldipyrro-
methane 4 was borylated under the standard conditions to
yield a mixture of diborylated and monoborylated dipyrro-
methanes 5 and 6 (Scheme 3). Without separation of unsta-
ble borylated intermediates, treatment of the crude mixture
with hexyl acrylate or ethyl acrylate in the presence of
[{Rh(OH)ACHTUNGRTNENG(U cod)}2] as catalyst in dioxane and water at 1008C
A
afforded the desired a-acrylate dipyrromethanes. Oxidation
with 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) in THF
at room temperature afforded the corresponding dipyrrin
products. Finally, treatment of the dipyrrins with triethyl-
tion prompted us to find optimal conditions for the boryla-
tion. Changing reaction conditions such as temperatures and
solvent did not improve the yield distinctly, but the yield in-
creased from 20 to 28% when 1.0 equiv of diboron reagent
was used instead of 2.0 equiv. The low yield probably results
from the instability of the BODIPY dyes under the reaction
conditions in the presence of an excess of bis(pinacolato)di-
boron. Eventually, we obtained the b,b’-diborylated and b-
monoborylated BODIPYs in 28 and 10% yield, respective-
ly.
Borylation of meso-mesityl dipyrromethane and BODIPY
occurs with exclusively at a and b positions, respectively,
and this allows complementary synthesis of a- and b-func-
tionalized BODIPY dyes. We then attempted introduction
of unsaturated ester functions by means of Rh-catalyzed
Heck-type addition (Scheme 2). Treatment of diboryldipyr-
AHCTUNGTRENaGNUN mine and BF3·OEt2 in toluene at room temperature fur-
nished the corresponding a-acrylate BODIPYs 2a and 2b in
16 and 22% yield or 2e and 2 f in 13 and 30% yield, respec-
tively, in four steps. Reaction with methyl 2,4-pentadienoate
allows further elongation of conjugation: using methyl 2,4-
pentadienoate provides 2c and 2d in 29% and 9% yield, re-
spectively. The ratio of the monosubstituted product to the
disubstituted product increased in comparison to that of the
borylated dipyrromethanes because of partial deborylation
during the Heck-type addition reaction.
To obtain b-substituted BODIPYs, we started from un-
substituted BODIPY 1 (Scheme 4). After borylation with
1.0 equiv of bis(pinacolato)diboron under iridium catalysis,
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5943

H. Shinokubo, A. Osuka et al.
X-Ray diffraction analysis of BODIPY dyes: Single crystals
suitable for X-ray diffraction studies were obtained for 2 f,
2d, and 3d. Figure 1 depicts the structures of these com-
pounds. The crystallographic data are summarized in
Table 2. The unsaturated ester moieties and the C9BN2
frameworks adopt a coplanar conformation for all com-
pounds, as clearly seen in the side views. This orientation
allows effective electronic conjugation between the C9BN2
framework and the double bonds. The lack of a clear dis-
À
tinction between the C C bond lengths of the dipyrrin back-
bone and the substituted double bonds for the three com-
pounds indicates substantial delocalization of the p systems.
The mesityl groups are perpendicular to the mean C9BN2
plane with dihedral angles of 76.65, 71.58, and 73.958 for 2 f,
2d, and 3d, respectively.
Photophysical characterization: UV/Vis absorption and
fluorescence spectra of the BODIPY dyes were recorded in
CH2Cl2. Figures 2 and 3 show the absorption and emission
spectra of the a- and b-substituted BODIPY dyes, along
with those of unsubstituted BODIPY 1. The a-substituted
dyes exhibit the typical absorption characteristics of
BODIPY dyes, that is, a narrow absorption band with a
maximum above 540 nm assigned to the S0–S1 transition and
a weak and broad absorption band attributed to the S0–S2
transition.[20] The absorption maxima are redshifted signifi-
cantly from 501 to 641 nm with extending conjugation, while
there is almost no change in spectral shape. The absorption
coefficients are increasingly enhanced compared with unsub-
stituted BODIPY 1. Disubstituted compounds 2b and 2d
have higher absorption coefficients than the corresponding
monosubstituted compounds 2a and 2c, that is, extended
conjugation at the a positions of BODIPY dyes has a hyper-
chromic effect. All the a-substituted BODIPYs show
narrow fluorescence emission bands with the mirror-image
shape of the absorption bands and small Stokes shifts. The
emission maximum of 2d is shifted to 651 nm, reaching into
the near-infrared spectral region while maintaining a rela-
tively high quantum yield (Ff =0.53). Mono- and disubstitut-
ed BODIPYs show good dispersion of UV/Vis absorbance
and fluorescence emission: the a-substituted BODIPYs are
colorful and brilliant to the naked eye when irradiated
under the UV light (Figure 4, 2a–2d).
Scheme 3. Synthesis of a-substituted BODIPYs without isolation of bory-
lated intermediates. i) bis(pinacolato)diboron, [[Ir(OMe)(cod)}2], dtbpy,
dioxane, 1008C; ii) hexyl or ethyl acrylate, [{Rh(OH)(cod)}2], dioxane,
H2O, 1008C; iii) DDQ/THF, then BF3·OEt2, Et3N, toluene; iv) methyl
2,4-pentadienoate, [{Rh(OH)(cod)}2], dioxane, H2O, 1008C.
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
In the case of b-substituted BODIPY dyes, the absorption
and emission spectra also exhibit substantial redshifts as the
conjugation extends, but the shapes tend to become broader
with increasing conjugation. The extinction coefficient of b-
substituted BODIPYs decreases compared with unsubstitut-
ed BODIPY 1, but the relative area of each S0–S1 absorp-
tion band increases and is comparable to that of a-substitut-
ed BODIPYs. This indicates that the oscillator strength is
also enhanced in the b-substituted series by the unsaturated
substituents. The sharpness of the fluorescence emissions is
characterized by full width at half maximum (fwhm), which
increases from 937 cmÀ1 for 1 to 1400 cmÀ1 for 3d. The
emission spectra of monosubstituted BODIPYs 3a and 3c
are distinctly broader than those of the corresponding disub-
stituted BODIPYs 3b and 3d. The emission quantum yields
Scheme 4. Synthesis of b-substituted BODIPYs without isolation of bory-
lated intermediates. i) bis(pinacolato)diboron, [{Ir(OMe)(cod)}2], dtbpy,
dioxane, 1008C; ii) hexyl acrylate, [{Rh(OH)(cod)}2], dioxane, H2O, RT;
iii) methyl 2,4-pentadienoate, [{Rh(OH)(cod)}2], dioxane, H2O, RT.
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
the reaction mixture was treated with hexyl acrylate or
methyl 2,4-pentadienoate directly in the presence of the rho-
dium catalyst in dioxane and water at room temperature to
give the desired b-substituted BODIPYs 3a in 7 and 3b in
7% yield or 3c in 3 and 3d in 1% yield. Unfortunately, the
yields of isolated products were low because the product
mixture contained saturated byproducts such as 3bꢀ due to
1,4-conjugate addition, and thus repeated chromatographic
purification was necessary.
5944
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Chem. Eur. J. 2009, 15, 5942 – 5949

Functionalization of Boron Dipyrrin Dyes
FULL PAPER
as brilliant as the a-substituted
BODIPYs (Figure 4, 3a–3d).
The absorption is blueshifted
and the emission redshifted in
comparison to the correspond-
ing a-substituted BODIPYs,
that is, the Stokes shifts of b-
substituted
BODIPYs
are
larger than those of the corre-
sponding a-substituted BODI-
PYs. Spectra data for all a- and
the b-substituted BODIPY dyes
in CH2Cl2 are collected in
Table 1.
Conclusions
We have developed the regiose-
lective borylation of meso-sub-
stituted dipyrromethane at the
a positions and BODIPY dyes
at the b positions. The high re-
gioselectivity of the borylation
procedure offers a new way to
synthesize different kinds of a-
or b-substituted BODIPY dyes
by means of transition metal
catalyzed reactions. Thus,
a
series of a- and b-substituted
BODIPY dyes with different
lengths of conjugation were
synthesized by rhodium-cata-
lyzed Heck-type addition of
borylated intermediates to acry-
late
and
2,4-pentadienoate
esters. The extended conjuga-
tion has significant effects on
the spectral properties of
BODIPY dyes and induces sub-
stantial redshifts of the absorp-
tion and emission spectra. The
a-substituted series exhibits
higher absorption coefficients
Figure 1. X-ray structures of 2 f, 2d, and 3d. a) Top and b) side views of 2 f; c) top and d) side views of 2d;
e) top and f) side views of 3d. Thermal ellipsoids at 50% probability.
Table 1. Spectral properties of BODIPY dyes in CH2Cl2.
UV/Vis
lmax [nm] emax [mÀ1 cmÀ1
Emission
Stokes shift [cmÀ1
]
Ff
]
Relative area[a] lem [nm] FWHM [cmÀ1
]
1
501
6.32ꢁ104
8.74ꢁ104
9.27ꢁ104
1.07ꢁ105
1.43ꢁ105
9.16ꢁ104
1.25ꢁ105
5.72ꢁ104
6.07ꢁ104
3.96ꢁ104
5.71ꢁ104
1.0
514
554
601
575
651
554
602
563
606
623
662
937
714
608
649
541
698
594
1565
1371
2279
1400
505
298
224
277
240
298
252
825
769
1902
692
0.92 (0.93)[b]
0.82
0.92
0.96
0.53
0.96
0.98
0.48
0.68
2a 545
2b 593
2c 566
2d 641
2e 545
2 f 593
3a 538
3b 579
3c 557
3d 633
1.13
1.30
1.33
1.75
1.17
1.43
1.45
1.48
1.36
1.83
and
yields,
fluorescence
sharp
quantum
fluorescence
peaks, and smaller Stokes shifts,
while the b-substituted series
shows lower absorption coeffi-
cients and fluorescence quan-
tum yields, broader fluores-
cence peaks, and larger Stokes
shifts with extending conjuga-
tion. These findings reveal that
0.019
0.054
[a] The relative area of each S0–S1 absorption band was obtained by integration of the spectrum after conver-
sion to the wavenumber scale. [b] Quantum yield of 1 in toluene reported in the literature.[18c]
decrease distinctly, and BODIPY 3d exhibits an emission
yield of only 0.054, about one-tenth of that of the corre-
sponding a-substituted BODIPY 2d. Consequently, it is not
properties of BODIPY dyes can be finely tuned not only by
extended conjugation but also by means of the position of
modification.
Chem. Eur. J. 2009, 15, 5942 – 5949
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5945

H. Shinokubo, A. Osuka et al.
Figure 2. UV/Vis absorption spectra of a- and b-substituted BODIPYs as
well as unsubstituted BODIPY 1 in CH2Cl2.
Figure 3. Normalized fluorescence emission spectra of a- and b-substitut-
ed BODIPYs as well as unsubstituted BODIPY 1 in CH2Cl2.
Table 2. Crystallographic details for 2 f, 2d, and 3d.
2 f
2d
3d
empirical formula
C28H29BF2N2O4 C30H29BF2N2O4 C30H29BF2N2O4
M
506.35
orthorhombic
Pbcn
14.175(3)
16.132(3)
24.474(7)
90.00
530.36
monoclinic
P21/c
21.529(4)
15.387(3)
8.1029(15)
90.00
530.36
monoclinic
P21/n
9.210(4)
17.869(7)
16.664(6)
90.00
crystal system
space group
a [ꢂ]
b [ꢂ]
c [ꢂ]
a [8]
b [8]
90.00
90.00
5596(2)
8
1.275
97.535(4)
90.00
2661.0(9)
4
1.324
0.096
100.783(7)
90.00
2693.9(18)
4
1.308
0.095
g [8]
V [ꢂ3]
Z
1calcd [gcmÀ3
]
m [mmÀ1
(000)
]
0.094
2262
Figure 4. Photograph of solutions of BODIPY dyes without (upper row)
and with UV irradiation (bottom row).
F
A
1112
1112
crystal size [mm]
2qmax [8]
0.60ꢁ0.50ꢁ0.20 0.80ꢁ0.60ꢁ0.15 0.50ꢁ0.20ꢁ0.20
55.0
50.0
56.0
Experimental Section
T [K]
123(2)
48861
6409
6409
351
90(2)
13770
4685
4685
357
90(2)
13793
5932
5932
394
total reflns
unique reflns
reflns used
parameters
absorption correc-
tion
R1
wR2
GOF
1
Instrumentation and materials: H NMR (600 MHz) spectra were record-
ed on a JEOL ECA-600 spectrometer. UV/Vis absorption spectra were
recorded on a Shimadzu UV-2550 spectrometer. Fluorescence emission
spectra were measured on Shimadzu RF-5300PC spectrometer. Quantum
yields were determined by the absolute method with a Hamamatsu
C9920-01 calibrated integrating-sphere system. Mass spectra were record-
ed on a Bruker microTOF. Recycling preparative GPC-HPLC was car-
ried out on JAI LC-908 with preparative JAIGEL-2H and 2.5H columns.
Unless otherwise noted, materials obtained from commercial suppliers
were used without further purification. Solvents used for spectroscopic
measurements were all of spectral grade.
none
none
none
0.0613
0.1894
1.077
0.0343
0.1028
1.087
0.0510
0.1419
1.026
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Chem. Eur. J. 2009, 15, 5942 – 5949

Functionalization of Boron Dipyrrin Dyes
FULL PAPER
Crystallographic data collection and structure refinement: Data for 2 f
were collected at low temperature (À1538C) on a Rigaku RAXIS-
RAPID with graphite-monochromated MoKa radiation (l=0.71069 ꢂ),
and data for 2d and 3d at À1838C on a Bruker SMART APEX with
graphite-monochromated MoKa radiation (l=0.71069 ꢂ). Details of the
crystallographic data are listed in Table 2. The structures were solved by
direct methods (Sir 97[21] or SHELXS-97[22]) and full-matrix least-squares
techniques (SHELXL-97).[22] CCDC 709675 (2 f), 709674 (2d) and 709676
(3d) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from the Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
was performed by column chromatography on silica gel (THF/hexane=
1/10) and recrystallization (CH2Cl2/hexane) to give BODIPY 2c
(powder) in 29% yield and BODIPY 2d (powder) in 9% yield.
BODIPY 2c: 1H NMR (CD2Cl2): d=2.08 (s, 6H; CH3 in mesityl), 2.35
(s, 3H; CH3 in mesityl), 3.75 (s, 3H; OCH3), 6.11 (d, J=15.1 Hz, 1H;
double bond), 6.49 (m, 1H; pyrrole H), 6.62 (d, J=4.1 Hz, 1H; pyrrole
1H), 6.64 (d, J=4.5 Hz, 1H; pyrrole H), 6.85 (d, J=4.1 Hz, 1H; pyrrole
H), 6.97 (s, 2H; ArH), 7.10 (dd, J=15.5, 11.5 Hz, 1H; double bond), 7.42
(d, J=15.6 Hz, 1H; double bond), 7.52 (dd, J=15.1, 11.0 Hz, 1H; double
bond), 7.84 ppm (s, 1H; pyrrole H); MS (MALDI-TOF): m/z 420.94
[M+], calcd m/z 420.26 [M+]; UV/Vis (CH2Cl2): lmax (e)=566 nm (1.07ꢁ
105 MÀ1 cmÀ1).
BODIPY 2d: 1H NMR (CD2Cl2): d=2.09 (s, 6H; CH3 in mesityl), 2.36
(s, 3H; CH3 in mesityl), 3.76 (s, 6H; OCH3), 6.12 (d, J=15.1 Hz, 2H;
double bond), 6.59 (d, J=4.1 Hz, 2H; pyrrole H), 6.88 (d, J=4.6 Hz, 2H;
pyrrole 1H), 6.98 (s, 2H; ArH), 7.11 (dd, J=15.6, 11.5 Hz, 2H; double
bond), 7.44 (d, J=15.6 Hz, 1H; double bond), 7.55 ppm (dd, J=15.1,
11.5 Hz, 1H; double bond); MS (ESI-TOF): m/z 553.2088 [M+Na+],
calcd m/z 553.2086 [M+Na+]; UV/Vis (CH2Cl2): lmax (e)=641 nm (1.43ꢁ
105 mÀ1 cmÀ1).
General procedure for the synthesis of a-substituted BODIPY dyes:
meso-Mesityldipyrromethane (264 mg, 1.0 mmol, 1.0 equiv), bis(pinacola-
to)diboron (508 mg, 2.0 mmol, 2.0 equiv), 4,4’-di-tert-butyl-2,2’-bipyridyl
(5.4 mg, 0.02 mmol, 0.02 equiv), and [{IrACHTNUTRGENNUG(cod)ACHTUNGTREN(NUGN OMe)}2] (6.63 mg,
0.01 mmol, 0.01 equiv) were added to a Schlenk flask, which was evacuat-
ed and purged with argon five times, and then charged with dried 1,4-di-
oxane (3.0 mL). The mixture was stirred at reflux for 24 h under argon
(oil-bath temperature: 100–1058C). After removal of the solvents under
vacuum, the residue was dissolved in CH2Cl2. The solution was filtered
through a short pad of Florisil (ca. 1.5 cm high, eluent: CH2Cl2), which
was washed with CH2Cl2 to remove the catalyst and insoluble salts. The
solvent was removed and the residue dried in vacuum to give the crude
borylated compounds (508 mg, a colorless glassy solid) without separa-
tion. The borylated compound (258 mg, 0.5 mmol, 1.0 equiv) and the cat-
BODIPYs 2e and 2 f: The general procedure was followed, but ethyl ac-
rylate was used instead of hexyl acrylate. Final purification was per-
formed by column chromatography on silica gel (CH2Cl2/hexane=1:10)
to give BODIPY 2e (oil) in 13% yield and BODIPY 2 f (powder, recrys-
tallized from CH2Cl2/hexane) in 30% yield.
alyst [{RhACHTUNGTRENNUNG(cod)(OH)}2] (11.4 mg, 0.025 mmol, 0.05 equiv) were added to
BODIPY 2e: 1H NMR (CDCl3): d=1.36 (t, 3H; J=7.4 Hz, CH3 in
ethyl), 2.09 (s, 6H; CH3 in mesityl), 2.36 (s, 3H; CH3 in mesityl), 4.31 (q,
2H; J=7.3 Hz; OCH2 in ethyl), 6.51 (d, J=3.7 Hz, 1H; pyrrole H), 6.56
(d, J=16.1 Hz, 1H; double bond), 6.62 (d, J=4.6 Hz, 1H; pyrrole H),
6.69 (d, J=4.1 Hz, 1H; pyrrole H), 6.79 (d, J=4.5 Hz, 1H; pyrrole H),
6.96 (s, 2H; ArH), 7.95 (s, 1H; pyrrole H), 8.10 ppm (d, J=16.5 Hz, 1H;
double bond); MS (ESI-TOF): m/z 431.1705 [M+Na+], calcd m/z
431.1717 [M+Na+]; UV/Vis (CH2Cl2): lmax (e)=545 nm (9.16ꢁ
104 mÀ1 cmÀ1).
BODIPY 2 f: 1H NMR (CDCl3): d=1.38 (t, 6H; J=6.8 Hz, CH3 in
ethyl), 2.09 (s, 6H; CH3 in mesityl), 2.36 (s, 3H; CH3 in mesityl), 4.32 (q,
4H; J=7.3 Hz; OCH2 in hexyl), 6.59 (d, J=16.0 Hz, 2H; double bond),
6.63 (d, J=4.6 Hz, 2H; pyrrole H), 6.83 (d, J=4.6 Hz, 2H; pyrrole H),
6.96 (s, 2H; ArH), 8.13 ppm (d, J=16.0 Hz, 2H; double bond); MS (ESI-
TOF): m/z 529.2058 [M+Na+], calcd m/z 529.2086 [M+Na+]; UV/Vis
(CH2Cl2): lmax (e)=593 nm (1.25ꢁ105 mÀ1 cmÀ1).
a Schlenk flask, which was evacuated and purged with argon three times,
and then charged with dioxane (2.5 mL), H2O (250 mL), and hexyl acry-
late (365 mL, 2.0 mmol, 4.0 equiv). The mixture was stirred at reflux for
24 h under argon (oil-bath temperature: 100–1058C). After removal of
the solvent, the residue was dissolved in 5 mL of THF, and DDQ
(114 mg, 0.5 mmol, 1.0 equiv) was added to the solution. After stirring at
room temperature for 15 min, the reaction mixture was quenched with a
saturated aqueous solution of NaHCO3 and extracted with CH2Cl2. The
organic layer was washed with water and dried over Na2SO4. Solvents
were removed and the residue was dissolved in 5 mL of toluene. After
purging with argon for 15 min, triethylamine (0.8 mL, 5.0 mmol,
10 equiv) was added to the reaction mixture followed by BF3·OEt2
(0.8 mL, 5.0 mmol, 10 equiv). The mixture was stirred at room tempera-
ture for 30 min, quenched with a saturated aqueous solution of NaHCO3,
and extracted with CH2Cl2. The organic layer was washed with water and
dried over Na2SO4. Solvents were removed and the residue was filtered
through a short pad of silica gel (eluent: CH2Cl2) to remove insoluble
salts and polar byproducts. The mixture was purified by GPC (BioRad
Bio-Beads SX-1, packed in a 3.0ꢁ60 cm gravity-flow column; eluent:
THF) to afford four major bands (in order of elution): 1) unidentified by-
product, 2) a,a’-diacrylate BODIPY 2b (oil, 71 mg, 22% yield), 3) a-
monoacrylate BODIPY 2a (oil, 39 mg, 16% yield), and 4) unsubstituted
BODIPY 1.
BODIPY 2a: 1H NMR (CDCl3): d=0.91 (t, 3H; J=6.8 Hz, CH3 in
hexyl), 1.25–1.69 (m, 8H; CH2 in hexyl), 2.09 (s, 6H; CH3 in mesityl),
2.36 (s, 3H; CH3 in mesityl), 4.23 (t, 2H; J=6.8 Hz; OCH2 in hexyl), 6.51
(d, J=4.1 Hz, 1H; pyrrole H), 6.56 (d, J=16.0 Hz, 1H; double bond),
6.62 (d, J=4.6 Hz, 1H; pyrrole H), 6.69 (d, J=4.1 Hz, 1H; pyrrole H),
6.79 (d, J=4.1 Hz, 1H; pyrrole H), 6.96 (s, 2H; ArH), 7.95 (s, 1H; pyr-
role H), 8.10 ppm (d, J=16.5 Hz, 1H; double bond); MS (ESI-TOF):
m/z 487.2345 [M+Na+], calcd m/z 487.2344 [M+Na+]; UV/Vis (CH2Cl2):
lmax (e)=545 nm (8.74ꢁ104 mÀ1 cmÀ1).
General procedure for the synthesis of b-substituted BODIPY dyes:
meso-Mesityl BODIPY (1, 100 mg, 0.32 mmol, 1.0 equiv), bis(pinacola-
to)diboron (81.7 mg, 0.32 mmol, 1.0 equiv), 4,4’-di-tert-butyl-2,2’-bipyridyl
(4.3 mg, 0.016 mmol, 0.05 equiv), and [IrACHTNUGTRNEUNG(cod)OMe]2 (5.3 mg, 0.008 mmol,
0.025 equiv) were added to a Schlenk flask, which was evacuated and
purged with argon five times, and then charged with dried dioxane
(3.0 mL). The mixture was stirred at reflux for 16 h under argon. After
removal of the solvent under vacuum, the residue was dissolved in
CH2Cl2. The solution was passed through a short pad of Florisil (ca.
1.5 cm high, eluent: CH2Cl2) to remove the catalyst and insoluble salts.
Then the crude product was transferred to a 50 mL round-bottomed-flask
and the solvent removed under vacuum to give the borylated products.
[{RhACTHUNTRGNE(UGN cod)(OH)}2] (7.3 mg, 0.016 mmol, 0.05 equiv) was added to the
flask, which was then purged with argon and charged with hexyl acrylate
(226 mL, 1.29 mmol, 4 equiv), H2O (300 mL), and dioxane (3.0 mL). The
mixture was stirred at room temperature for 24 h under argon. The sol-
vent was evaporated under vacuum, and the crude product purified by
chromatography on silica gel (CH2Cl2/hexane=3/1) to provide BODIPY
3a (oil) in 7% yield and BODIPY 3b (powder) in 7% yield.
BODIPY 3a: 1H NMR (CDCl3): d=0.88 (t, J=6.8 Hz, 3H; CH3 in
hexyl), 1.25–1.65 (m, 8H; CH2 in hexyl), 2.10 (s, 6H; CH3 in mesityl),
2.38 (s, 3H; CH3 in mesityl), 4.14 (t, J=6.8 Hz, 2H; OCH2 in hexyl), 6.17
(d, J=16.0 Hz, 1H; double bond), 6.54 (d, J=3.7 Hz, 1H; pyrrole H),
6.73 (s, 1H; pyrrole H), 6.77 (d, J=4.1 Hz, 1H; pyrrole H), 6.97 (s, 2H;
ArH), 7.47 (d, J=16.0 Hz, 1H; double bond), 8.00 (s, 1H; pyrrole H),
8.03 ppm (s, 1H; pyrrole H); MS (ESI-TOF): m/z 487.2338 [M+Na+],
BODIPY 2b: 1H NMR (CDCl3): d=0.91 (t, 6H; J=6.8 Hz, CH3 in
hexyl), 1.25–1.74 (m, 16H; CH2 in hexyl), 2.09 (s, 6H; CH3 in mesityl),
2.36 (s, 3H; CH3 in mesityl), 4.26 (t, 4H; J=6.9 Hz; OCH2 in hexyl), 6.59
(d, J=16.0 Hz, 2H; double bond), 6.63 (d, J=4.1 Hz, 2H; pyrrole H),
6.83 (d, J=4.6 Hz, 2H; pyrrole H), 6.96 (s, 2H; ArH), 8.14 (d, J=
16.0 Hz, 2H; double bond); MS (ESI-TOF): m/z 641.3316 [M+Na+],
calcd m/z 641.3339 [M+Na+]; UV/Vis (CH2Cl2): lmax (e)=593 nm (9.27ꢁ
104 mÀ1 cmÀ1).
BODIPYs 2c and 2d: The general procedure was followed, but methyl
2,4-pentadienoate was used instead of hexyl acrylate. Final purification
Chem. Eur. J. 2009, 15, 5942 – 5949
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H. Shinokubo, A. Osuka et al.
calcd m/z 487.2344 [M+Na+]; UV/Vis (CH2Cl2): lmax (e)=538 nm (5.72ꢁ
104 mÀ1 cmÀ1).
H. Sunahara, T. Nagano, Y. Wada, N. V. Tkachenko, H. Lemmetyi-
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BODIPY 3b: 1H NMR (CDCl3): d=0.89 (t, J=6.9 Hz, 6H; CH3 in
hexyl), 1.30–1.70 (m, 16H; CH2 in hexyl), 2.10 (s, 6H; CH3 in mesityl),
2.39 (s, 3H; CH3 in mesityl), 4.15 (t, J=6.4 Hz, 4H; OCH2 in hexyl), 6.21
(d, J=16.0 Hz, 2H; double bond), 6.79 (s, 2H; pyrrole H), 6.99 (s, 2H;
ArH), 7.46 (d, J=16.0 Hz, 2H; double bond), 8.12 ppm (s, 2H; pyrrole
H); MS (ESI-TOF): m/z 641.3343 [M+Na+], calcd m/z 641.3339
[M+Na+]; UV/Vis (CH2Cl2): lmax (e)=579 nm (6.07ꢁ104 mÀ1 cmÀ1).
BODIPYs 3c and 3d: The general procedure was followed, but methyl
2,4-pentadienoate was employed instead of hexyl acrylate. After removal
of the solvent, the residue was purified by column chromatography on
silica gel (THF/hexane=1/10) to provide BODIPY 3c (powder, recrys-
tallized from CH2Cl2/hexane) in 3% yield and BODIPY 3d (powder, re-
crystallized from CH2Cl2/hexane) in 1% yield.
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1
BODIPY 3c: H NMR (CDCl3): d=2.11 (s, 6H; CH3 in mesityl), 2.38 (s,
3H; CH3 in mesityl), 3.75 (s, 3H; OCH3), 5.89 (d, J=15.1 Hz, 1H;
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(s, 2H; ArH), 7.35 (dd, J=15.1, 10.5 Hz, 1H; double bond), 7.96 (s, 1H;
pyrrole H), 8.03 ppm (s, 1H; pyrrole H); MS (MALDI-TOF): m/z 420.75
[M+], calcd m/z 420.26 [M+]; UV/Vis (CH2Cl2): lmax (e)=557 nm (3.96ꢁ
104 mÀ1 cmÀ1).
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1
BODIPY 3d: H NMR (CDCl3): d=2.12 (s, 6H; CH3 in mesityl), 2.39 (s,
3H; CH3 in mesityl), 3.75 (s, 3H; OCH3), 5.91 (d, J=15.5 Hz, 2H;
double bond), 6.62–6.70 (m, 6H; pyrrole 2H and double bond 4H), 7.00
(s, 2H; ArH), 7.35 (dd, J=15.5, 10.1 Hz, 2H; double bond), 8.07 ppm (s,
1H; pyrrole H); MS (MALDI-TOF): m/z 530.18 [M+], calcd m/z 530.37
[M+]; UV/Vis (CH2Cl2): lmax (e)=633 nm (5.71ꢁ104 mÀ1 cmÀ1).
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This work was partly supported by a Grant-in-Aid for Scientific Research
(No. 18685013) from MEXT, Japan. Financial support from the Sumito-
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Functionalization of Boron Dipyrrin Dyes
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Received: December 4, 2008
Revised: February 25, 2009
Published online: May 5, 2009
Chem. Eur. J. 2009, 15, 5942 – 5949
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
5949